A position sensor can detect the presence and location of a touch by a finger or by an object such as a stylus within an area of an external interface of the position sensor. In a touch sensitive display application such as a touch screen, the position sensor enables direct interaction with what is displayed on the screen rather than indirectly with a mouse or touchpad. Position sensors can be combined with devices having a display, including but not limited to computers, personal digital assistants, satellite navigation devices, mobile telephones, portable media players, portable game consoles, public information kiosks, and point of sale systems. Position sensors have also been used as control panels on various appliances.
There are a number of different types of touch screens, such as resistive touch screens, surface acoustic wave touch screens, capacitive touch screens, etc. A capacitive touch screen, for example, may include an insulator coated with a transparent conductor in a particular pattern. A change in capacitance may occur when a finger or an object touches the surface of the screen. This change in capacitance may be processed by a controller to determine the position of the touch.
In a mutual capacitance configuration, for example, an array of conductive drive electrodes or lines and conductive sense electrodes or lines can be used to form a grid of capacitive nodes. Nodes are formed where drive and sense electrodes overlap and the sense electrodes are capacitively coupled with the drive electrodes. A pulsed or alternating voltage applied on the drive electrode induces a charge on the sense electrode. The amount of induced charge may be susceptible to external influence, such as from a nearby finger or object. When a finger or an object touches the surface of the screen, capacitance changes. The capacitance change may arise from changes to the fringe field between the drive and sense electrodes or outside the areas in which the drive and sense electrodes overlap. The capacitance change at each node on the grid can be measured to determine the location or position of the touch.